A device for locking and unlocking a plug on a frame using a wrench is known through document FR-A-2780996 and document FR-A-2898614.
The locking and unlocking device as described in either of these two documents entails a lock connected to the plug and a wrench with a maneuvering arm, one end of which bears a socket that can be introduced into an opening of the cover in order to access the lock. The lock has a rotor mounted to rotate in the plug and, at one of its ends, bears a bolt that cooperates with a keeper of the frame. The other end of the rotor can be coupled with the socket of the wrench to make possible the pivoting of the bolt around the longitudinal axis of the rotor, between a locking position and the bolt is captured by the keeper, in which the wrench can freely come out of the opening of the plug, and an unlocking position in which case the bolt is disengaged from the keeper and the wrench is held captured in the opening of the plug.
This known device has the drawback that unauthorized persons can make a wrench with a shape similar to the specific wrench used in this device in order to access the rotor for moving the bolt and can unlock the lock with respect to the keeper of the frame.